Open loop all the time? New O2/AF sensors.

I have noticed that my truck is always in open loop. I have a scan gauge and it says it's always open even after warming up.

I just replaced the O2 and AF sensors as they were original to the truck and I'm at 207K mi. I tested the first O2 (pre cat) and it was out of spec (no SES light) the second sensor tested ok.

My milage is still pretty crappy. I have new plugs. Wires tested fine. Fuel filter is new. Coils are fine. Air filter is fine.

What are you guys using to see Fuel Trim Levels? Maybe there's something else I'm missing? Maybe I'm towing a drag chute?

 

Coolant temp (for ECU) is a main input for closed loop operation. Make sure that it is working. When you say the 1st O2 was out of spec, what exactly do you mean?

 

You are gonna choke off the cat pushing all that raw fuel into it. Cats are expensive. Find out why you are open loop and save lots of money.

 

Does it show the monitor status for each system?

 

Manual says for both sensors to be functioning properly they need to have a resistance of 12-16(?) ohms. The rear sensor did, the front (first) sensor tested bad at I think 1.5 or 3.5 ohms.

Scan Guage just shows the loop as closed or open.

Maybe I need a different OBD2 reader.

When I say bad mileage I’m talking 13-14 mpg. And that may be normal I dunno. I thought that by replacing a bad O2 sensor I’d see some increase in mileage. Even if it were 1-2 mpg..

 

A gauge is not going to diagnose your possible issue properly. You have to use a proper scanner. If you are getting 13-14 mpg it may be a gauge issue rather than an actual issue you are having. Get a good scanner and recheck it.

 

Can you recommend a particular scan tool that will do more than a scan gauge? There are some Bluetooth ones that look good. Unless your talking about a real automotive tool type scanner...

 

Well I can't remember which one we use as a backup at the shop I work at, but I would make sure you look into a real automotive scanner because those are made to give accurate real time data.

I can check tomorrow and let you know on the BT one that we use.